Investigation of gasochromic properties in tungsten oxide thin films prepared by glancing angle deposition using electron beam evaporation

Nano-layers of zinc sulfide on glass substrates were prepared by physical vapor deposition (PVD) method, under high vacuum (HV) conditions, with different deposition angles of 0, 25, and 35° at 300 K temperature. Thickness of the layers was measured 73 nm, by quartz crystal method. The nanostructures of the films were obtained, by using X-ray diffraction (XRD) and atomic force microscopy (AFM) methods. Optical reflectance and transmittance of the layers were measured in the wavelength range of 300–1100 nm by a spectrophotometer. Kramers-Kronig relations were used to calculate the optical constants. Fraction of voids were calculated by Aspens theory. By increasing deposition angle, more voids are formed on layers and structure of layers has changed from homogeneous to heterogeneous. In this work, the influence of deposition angle on optical properties, structural changes, and the relation between nano structures and optical properties of ZnS nano-layers are investigated. The samples prepared under higher deposition angles showed smaller absorption coefficient. Optical properties are studied using full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the generalized gradient approximation (GGA) was used for the exchange-correlation potential calculation. The calculation results are compared with experimental data. Possible energy transitions are also reported. An average value of 2.40-eV band gap for the layers produced in this work has been deduced which is also calculated from FP-LAPW method, and obtained about 2.2 eV.

In this work, MgF2 single-layers are designed by the Essential Macleod program and prepared by physical vapour deposition (PVD) using the glancing angle deposition (GLAD) technique. The samples were prepared at 0°, 25°, 70°, and 80° deposition angles. The optical, morphological, and structural properties of the films studied by UV–VIS, field emission scanning electron microscope (FESEM), and X-ray diffraction (XRD). The crystallinity of the grown films decreased upon increasing deposition angle, which is characteristic of GLAD technique. A good agreement was found between optical transmission spectra of the designed and the deposited films. The refractive index of samples decreased from 1.46 to 1.29 as the deposition angle increased from 0° to 80°. The extinction coefficient of samples increased from 0.0027 to 0.0052 as the deposition angle increased from 0° to 80°.

Exploiting the dodecane and ozone sensing capabilities of nanostructured tungsten oxide films

Electrochromic materials change color reversibly by applying an external DC voltage. One among the many emerging application of electrochromics is the smart windows. Tungsten oxide (WO3) is well studied and the most versatile electrochromic material. In the present communication, the tungsten oxide thin films have been prepared (at 300K) on lexan (poly carbonate) substrates by reactive DC magnetron sputtering technique using neon as sputter gas for the first time. The electrochromic performance of the WO3 thin films (in the thickness range 190 nm to 712 nm) have been studied with two aqueous electrolytes: 1M HCl and 1M Li2SO4 in a three electrode electrochemical cell. The highest coloration efficiency (at 860 nm) of the neon sputtered WO3 achieved is 273 cm2 C−1 by lithium intercalation. The inference of the present investigation is that: sputtering with neon on lexan yields tungsten oxide thin films which have high coloration efficiency, high contrast, fast coloration and are highly stable.

Smart glass electrochromic device fabrication of uniform tungsten oxide films from its powder synthesized by solution combustion method

The colouration efficiency in the electrochromic devices depends upon the amount of intercalating charge in the tungsten oxide (WO3−x) thin films. One of the physical properties of the film that significantly influence the intercalating charge is the film density. In this paper, the dependence of intercalated charge in WO3−x thin films on the film density is reported. The amorphous tungsten oxide thin films have been prepared by electron beam evaporation at three substrate temperatures: 300, 470 and 570 K. With increasing substrate temperature, the refractive indices of the films increase. The relative film density calculated from the refractive index using the Lorentz–Lorentz relationship increases with the substrate temperature. With increasing density of the WO3 thin films, the diffusion coefficients of protons and the amount of intercalated charge decrease. The intercalated charge in the coloured electrochromic thin films brings about a change in the surface work function of the thin film; the difference in the surface work function (between the coloured and the bleached states) is measured by the Kelvin probe. In the present investigation, an intercalating charge of 59, 48 and 39 mC cm−2 brings about a change of 0.24, 0.16 and 0.13 eV in the surface work function of the WO3 thin films.

The growth and resulting crystallography of Cu nanowire arrays fabricated using glancing angle deposition are studied. On native oxide Si(100), the nanowires exhibited a strong (110) texture for a deposition angle θ=75° with rotational symmetry of the low energy Cu[111] about the long axis. On hydrogen-terminated Si(110), the wires are epitaxial with the substrate. The critical height for epitaxial growth is maximal at θ=35°, and decreases rapidly with increasing deposition angle. Based on the growth mechanisms in glancing-angle-deposited materials, the theory of growth mode in epitaxial thin films, and the observations about texture formation in epitaxial and nonepitaxial Cu nanowires; we discuss the observed growth modes in epitaxial nanowire arrays.

Response time of nanostructured relative humidity sensors

Tungsten oxide (WO 3 ) thin-films fabricated on glass slides have been proven to generate lossy mode resonances (LMRs) in the visible region. Obtained devices were characterized in transmission by lateral incidence of light on the edge of glass slides. Resonances at both TE and TM polarizations were analyzed for different thicknesses and in different deposition conditions. Moreover, it was successfully proved that WO 3 coated glass slides present a high sensitivity to refractive index, which opens the path to the application of this structure in the domain of optical sensors

In this investigation, vanadium doped tungsten oxide (V : WO3) thin films are prepared at room temperature by reactive dc magnetron sputtering employing a tungsten–vanadium ‘inlay’ target. In comparison with pure sputtered tungsten oxide thin films, 11% vanadium doping is observed to decrease the optical band gap, enhance the colour neutral property, decrease the coloration efficiency (from 121 to 13 cm2 C−1), increase the surface work function (4.68–4.83 eV) and significantly enhance the photocatalytic efficiency in WO3 thin films. These observations suggest that (i) vanadium creates defect levels that are responsible for optical band gap reduction, (ii) multivalent vanadium bonding with terminal oxygen in the WO3 lattice gives rise to localized covalent bonds and thus results in an increase in the work function, and (iii) a suitable work function of V : WO3 with ITO results in an enhancement of the photocatalytic activity. These results on electrochromic and photocatalytic properties of V : WO3 thin films show good promise in the low maintenance window application.

Electroforming-less and multi-level resistive switching characteristics in tungsten oxide thin film

Morphology and crystal texture in tilted columnar micro-structured titanium thin film coatings

Optimizing ultrasonic mist vapor deposition parameters toward facile synthesis of tungsten oxide nanofibers

Among chromogenic materials, tungsten trioxide (WO3) is of great interest. It is a colourlesssemiconductor characterised by a lack of toxicity and high chemical stability. WO3 exhibits gasochromicproperties, meaning that the material undergoes reversible changes in optical properties when it isexposed to gas. These properties make tungsten oxide a suitable material for sensing applications. Thispaper presents the results of an analysis of the surface, structural and optical properties of tungstenoxide thin films fabricated by electron beam evaporation and annealed at 400C to 800C. Opticalproperties, including gasochromic properties, were determined from light transmission spectra inan atmosphere containing hydrogen at the concentrations ranging from 50 ppm to 500 ppm. Theoptical properties of WO3 films without and with a palladium catalyst layer are applied. Annealing thesamples at temperatures above 400C resulted in crystallisation of the layers, and further post-processmodification at 800C led to sublimation, the formation of islands of crystalline grains of large size anda significant deterioration in optical properties. A change in the light transmission coefficient occurredfor all samples with the catalyst layer applied after the introduction of a hydrogen-argon mixture.Based on the results, it can be concluded that the layers annealed at 400C had the best gasochromic properties due to the greatest changes in light transmission under hydrogen. The study confirmsthat it is possible to improve the gasochromic response of tungsten trioxide thin films produced byelectron beam evaporation using thermal modification, which, to the best of current knowledge, hasnot previously been achieved.Keywords: electronics, WO3, electron beam evaporation, gasochromic properties, optical properties,annealing, optical hydrogen gas sensor

Abstract. Glancing angle deposition (GLAD) is a physical vapor deposition (PVD) process using a substrate that rotates tilted at an angle to the evaporation source. Depending on the deposition conditions, it provides the controlled formation of regular nanostructures during the PVD process. As a result, a wide variety of shapes, such as spirals or vertical columns, can be easily fabricated in the nanometer range. For this reason, GLAD has already been proven reliable in the production of optical coatings with very low reflectance in a broad spectral range. This paper examines the morphology of tantalum nanostructures deposited on planar silicon substrates by electron beam evaporation. The prepared samples are characterized by scanning electron microscope (SEM) images at a breaking edge with respect to the layer structure and by focused ion beam (FIB) SEM images of the cross-sectional areas with respect to the porosity. The porosity can be used to model the optical properties of the thin film with the effective medium theory (EMT). Our work studies the relationship between the evaporation parameters (growth pitch and deposition angle) and thin film morphology of tantalum so that in future work the optical properties can be linked to the deposition parameters, which in turn can be chosen to achieve highly absorbent infrared radiation layers, e.g., for infrared sensors. It was shown that the porosity across the film thickness of both columnar and screw-like thin films is nearly constant, whereas the porosity profiles of spiral structures show a periodic pattern, the period of which seems to depend on the growth pitch.